I think you suffer from what i would call straight facing face.You tend to try to make all the feature of the face.Face the viewer instead of actually follow the image i think it might be due if i am correct that you tend to spend to much time not looking back at the reference.It also tricky to draw head from a low angle because we tend to rely on memory because we are not accustom to view the face in that angle it just the brain trying to be lazy it not all your fault you just need to be aware of it and look back at the reference.Remember that angle you put in the early stage of a drawing are the fundation of the image if there wrong you will have a drawing that feel strange.Forget shading and focus on construction, measuring and proportion.Shading is atm in your leg i would recommend that you ignore it and concentrate on focusing on the aspect i talk about.

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